The present invention relates to method apparatus for driving an optical pickup of an optical information recording and reproducing apparatus, and more particularly to a method and apparatus for driving an optical pickup of an optical information recording and reproducing apparatus having the optical pickup movable on an information track of an optical information recording medium having information tracks formed thereon side by side and optical pickup moving means for intermittently moving the optical pickup.
A prior art optical information recording and reproducing method is first explained.
FIG. 1 shows an optical information recording and reproducing apparatus. In FIG. 1, numeral 1 denotes an optical information recording medium which is reciprocated in an X direction during recording and reproducing operations, numeral 2 denotes information tracks which includes first to nth information tracks 21-2n, numeral 3 denotes an optical pickup, numeral 7 denotes an objective lens, and .DELTA.A denotes a movable range of the objective lens 7 for tracking. The objective lens 7 is moved by an actuator (which usually comprises a coil and a magnet), not shown. Numeral 4 denotes optical pickup moving means, numeral 5 denotes a ball screw, and numeral 6 denotes a stepping motor. The optical pickup 3 is movable in a Y direction by the optical pickup drive means. A symbol .theta. represents an angle between the X direction of the movement of the optical information recording medium 1 and the information tracks 2 due to a setting error (skew angle), .DELTA.T represents a distance of movement of the objective lens 7 from one information track to an adjacent track (for example, from a track 2k to a track 2k+1), and .DELTA.L represents a distance of movement in the Y direction of the optical pickup 3 or the objective lens 7 for recording or reproducing information on or from one information track (for example, the track 2k) when the optical information recording medium 1 is reciprocated in the X direction.
When information is to be recorded or reproduced, the optical information recording medium 1 is normally reciprocated in the X direction and the information is recorded or reproduced on or from the information track 2 by using the objective lens 7. Because of the skew angle .theta. due to the setting error, the objective lens 7 is moved in the Y direction while the medium 1 is moved in the X direction in order to record or reproduce one track (for example, the track 2k) of information, and if the track cannot be traced by the Y direction movement of the objective lens 7, the optical pickup 3 is intermittently moved to prevent the objective lens 7 from being deviated from the information track 2k.
The movable range .DELTA.A of the objective lens 7 and the distance .DELTA.L of movement of the objective lens 7 which is to be moved for recording and reproducing information due to the skew angle usually has the following relationship: EQU .DELTA.A&lt;.DELTA.L
As a result, the optical pickup 3 must be moved in the Y direction by the optical pickup drive means 4. Assuming that the optical pickup 3 is moved by a distance .DELTA.P' in one intermittent movement, the objective lens 7 must be moved by a distance -.DELTA.P' (the same distance as the distance of movement of the optical pickup 3 but in the opposite direction) in order to prevent the objective lens 7 from being deviated from the information track 2k.
Usually, the distance of movement .DELTA.P' of the optical pickup 3 and the distance of movement .DELTA.T of the objective lens 7 when it is moved from one information track to the adjacent track are selected to meet a relationship EQU .DELTA.P'&gt;.DELTA.T
because the larger .DELTA.P' is, the larger may be the Y direction velocity of the optical pickup 3.
FIG. 2 shows a characteristic curve of the distance of movement of the optical pickup versus time in the optical pickup drive method for the prior art optical information recording and reproducing apparatus. In FIG. 2, .DELTA.P" represents a secondary oscillation amplitude generated when the optical pickup 3 is moved in the Y direction by the distance .DELTA.P'. If .DELTA.P' is too large compared to .DELTA.T, the secondary oscillation amplitude .DELTA.P" is equal to .DELTA.T or .DELTA.P"&gt;.DELTA.T. Accordingly, the distance of movement of the objective lens 7 which is moved in the opposite direction to the optical pickup 3 must be determined by taking -.DELTA.P' as well as the secondary oscillation amplitude .DELTA.P" of the optical pickup 3 into consideration. Otherwise, the objective lens 7 is moved to the adjacent information track and the information will not be correctly recorded or reproduced. When .DELTA.P" is smaller than .DELTA.T, .DELTA.P" cannot be neglected because the objective lens 7 may be moved beyond the current information track.
Thus, the object lens 7 must be instantly moved in the opposite direction upon the movement of the optical pickup 3. Thus, a large current is usually supplied to the coil of the actuator which drives the objective lens 7 to increase the speed of the objective lens 7.
However, in such a prior art method for driving the optical pickup, the wire diameter of the coil of the actuator is large, the mass of the actuator is large, a large current is required and a large magnet for the actuator is required. As a result, it is not suitable to the high speed drive of the objective lens.